Scanned beam video projectors ideally project a grid of evenly spaced virtual pixels onto a surface. Due to the geometry, optical path distortion, and changing scanner velocity, each virtual pixel is scanned across the surface in a continually changing time period. One challenge of digital scanned beam projection is matching this continually changing time period to the fixed clock period of a digital control system. Another challenge of laser based scanned beam video projectors is that generating a continuous low light power from a laser is far less efficient than generating higher laser powers. It is much more efficient to generate low optical powers by modulating between off and a higher optical power. This modulation can reduce the maximum brightness of the video content.
In the past, scanning laser based video projectors have used constant sample frequency digital-to-analog converters (DACs) to generate laser drive waveforms. To resynchronize these waveforms with the continually changing virtual pixel frequency, digital upsampling and interpolation may be used. Upsampling involves a far higher DAC sample rate which has a high bus transaction power cost. Interpolation may cause a loss of image sharpness particularly for computer generated video content. Modulation of the laser optical power has been tried in two orthogonal ways both using a constant frequency DAC. The first method provides each non-zero DAC sample with the same waveform. This method shows a reduction in laser speckle artifacts and an increase in efficiency but drastically reduces the maximum brightness of the projector. The second method zeroes all but one DAC sample in each pixel period. This method shows an increase in laser efficiency but shows a reduction in brightness and significant video artifacts since the active sample is not locked to the position of each pixel.
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